Terminal Impedance and Generalized Two-Wire-Line Theory

Conventional transmission-line theory takes no account of variations in the parameters of the line and of coupling near a terminating impedor, or near any other change in its uniform properties. A theory is derived which substitutes for these effects a simple terminal-zone network of lumped series and shunt elements which may be evaluated for each type of termination or discontinuity. The apparent terminal impedance Zsa(which is the impedance actually measured on a lossless line at a distance λ/2 from the termination) consists of this network in combination with the theoretical, isolated impedance, Zs, of the load. Zsafor a fixed termination with a given Zsmay vary greatly with the nature of the connection to the line, the relative orientation of line and load, and the type of line and its dimensions.